Refrigeration appliance including a compartment that can be heated and cooled

ABSTRACT

A refrigeration appliance, in particular a household refrigeration appliance, includes at least first, second and third storage chambers, and a refrigerant circuit on which the following are connected in series between a pressure connection and a suction connection of a compressor: a condenser, a first expansion valve, a first heat exchanger of the first storage chamber, a second expansion valve, a second heat exchanger of the second storage chamber, a third heat exchanger assigned to the third storage chamber, and a control circuit for controlling operation of the compressor and the expansion valves. The third heat exchanger is connected in series downstream of the second heat exchanger. The control circuit is configured to maintain a higher storage temperature in the third storage chamber than in the second storage chamber. A method for operating the refrigeration appliance and a computer program product are also provided.

The present invention relates to a refrigeration appliance, in particular a household refrigeration appliance, having at least one storage compartment which can optionally be heated or cooled.

Such a refrigeration appliance is known from DE 10 2016 032 986 A, for instance. With this known refrigeration appliance, heat exchangers of the compartment which can be heated and cooled and of a first cooled compartment with each in case an upstream and a downstream expansion valve are arranged in line sections of the refrigerant circuit which are parallel to one another and ii both sections lead to the evaporator of a second cooled compartment. Since the pressure in the last evaporator is lower than in any of the heat exchangers, the second cooled compartment is inevitably the coldest, i.e. the first cooled compartment is considered to be the normal refrigerator compartment, the second to be the freezer compartment. Four expansion valves are therefore required in order to realize three different temperature zones in the refrigeration appliance; this renders the known refrigeration appliance relatively expensive. Moreover, its refrigerant circuit is sensitive to overflows from the heat exchangers, which necessitates a sensitive and accordingly expensive control.

An object of the present invention is therefore to create a refrigeration appliance with a storage compartment which can be heated and cooled, which is assembled in a simpler manner and can accordingly be realized cost-effectively. A further object is to create an operating method for such a refrigeration appliance.

The object is achieved on the one hand in that, with a refrigeration appliance, in particular a household refrigeration appliance, having at least a first, a second and a third storage chamber, a refrigerant circuit, to which are connected in series one behind the other between a pressure connection and a suction connection of a compressor:

-   -   a condenser,     -   a first expansion valve,     -   a first heat exchanger of the first storage chamber,     -   a second expansion valve, and     -   a second heat exchanger of the second storage chamber;         a third heat exchanger assigned to the third storage chamber and         a control circuit for controlling the operation of the         compressor and the expansion valves, the control circuit is         configured to maintain a higher storage temperature in the third         storage chamber than in the second storage chamber.

With this setup, two expansion valves are still required in order to adjust the mass flow through the first heat exchanger and the pressures in the first and in the second heat exchanger, but a temperature regulation of the third storage chamber can take place without recourse to expansion valves, by, depending on requirement, only refrigerant vapor or vapor and liquid refrigerant in variable parts being allowed to pass from the second into the third heat exchanger. An overflow of the second heat exchanger does not result here in malfunctioning and need not be suppressed by means of control; instead, it forms part of the normal operation of the refrigeration appliance, by it enabling the third heat exchanger to be supplied with liquid refrigerant.

The connection between the second and third heat exchanger does not require a further expansion valve; on the contrary, this connection should be as free as possible of restrictions which impede the transfer of refrigerant to the third heat exchanger or favor a pressure difference between the second and third heat exchanger. The smallest free cross-section of a refrigerant pipe connecting the heat exchangers is preferably substantially the same size, in any case at least half as large as an average free cross-section of lines of the heat exchangers.

It should be possible to adjust the rotational speed of the compressor, preferably continuously, to a plurality of values, so that as a result of uninterrupted operation of the compressor, temporal fluctuations in the temperature in the storage chambers and the overconsumption of electrical energy associated with these fluctuations can be minimized.

The control circuit is preferably configured to increase the rotational speed of the compressor when the temperature in the second storage chamber is above a target value and/or to reduce the rotational speed when the temperature in the second storage chamber is below a target value. By increasing the rotational speed of the compressor, the pressure in a suction line leading to the compressor and via this also the pressure in the second and third heat exchanger can be reduced. Since the cooling effect of the third heat exchanger is largely not based on the evaporation of liquid refrigerant but instead on through-flowing vapor which originates from the second heat exchanger, the change in rotational speed at the most marginally influences the cooling effect of the third heat exchanger; the drop in pressure by contrast has a direct effect on the evaporation of the refrigerant which takes place in the second heat exchanger.

The afore-cited target values may be identical; they may however also define the limits of an interval within which the rotational speed of the evaporator remains unchanged.

In order to regulate the temperature in the third storage chamber, the control circuit is preferably configured to enlarge the degree of opening of the first expansion valve when the temperature in the third storage chamber is above a target value, and/or to reduce the degree of opening of the first expansion valve when the temperature in the third storage chamber is below a target value. Although the first expansion valve and the third heat exchanger in the refrigerant circuit are separated in one direction by two heat exchangers and the second expansion valve and in the other by the compressor, an adjustment of the first expansion valve has a surprising effect above all in the third heat exchanger. Opening the first expansion valve initially brings about a reduction in the choke effect of the entire refrigerant circuit. The pressure in the second and third heat exchanger however only changes a little as a result, since the extent to which this pressure increases causes the throughput of the compressor also to grow with a constant rotational speed. As a result, the main consequence of the opening of the first expansion valve is an increased flow of liquid refrigerant through the second expansion valve and as a result, at the latest after the second heat exchanger is completely filled with liquid refrigerant, an increased supply of liquid refrigerant to the third heat exchanger and thus an increased cooling of the third storage chamber.

The control circuit can also be configured to enlarge the degree of opening of the second expansion valve when the temperature in the third storage chamber is ii above a target value, and/or to reduce the degree of opening of the second expansion valve when the temperature in the third storage chamber is below a target value.

A decision as to which of these two possibilities is followed is expediently made on the basis of a comparison of the target temperature of the first storage chamber with the ambient temperature.

In order to control the temperature in the first storage chamber, the control circuit can be configured to enlarge the degree of opening of the second expansion valve when the temperature in the first storage chamber is above a target value and/or to reduce the degree of opening of the second expansion valve when the temperature in the first storage chamber is below a target value.

Alternatively, the control circuit can be configured to enlarge the degree of opening of the first expansion valve when the temperature in the first storage chamber lies below a target value and/or to reduce the degree of opening of the first expansion valve when the temperature in the first storage chamber is above a target value.

Here the selection between the alternatives can also be made on the basis of a comparison of the target temperature of the first storage chamber with the ambient temperature.

A third expansion valve, a fourth heat exchanger of a fourth storage chamber and a fourth expansion valve can be connected in series with one another and in parallel with the first expansion valve, the first heat exchanger and the second expansion valve. A number of compartments which can optionally be heated or cooled can therefore be produced in the refrigeration appliance.

The temperatures in these compartments can be adjusted independently of one another by adjusting the vaporization pressures with the aid of the upstream and downstream expansion valves.

With a refrigeration appliance having a fourth storage chamber, as described above, the degree of opening of the third expansion valve can also be enlarged ii when the temperature in the third storage chamber is above a target value, and/or the degree of opening of the third expansion valve can be reduced when the temperature in the third storage chamber is below a target value.

If desired, further storage chambers, in each case with an assigned heat exchanger and the expansion valves arranged upstream and downstream hereof in a branch of the refrigerant circuit, can be provided.

A fan for driving the air exchange between the heat exchanger and the storage chamber can be assigned to at least one of the heat exchangers. Such a fan is advantageous in terms of intensifying the heat exchange with the storage chamber and thus in reaching a high exchanging capacity with a compact heat exchanger. They are not essential in order to control the cooling of the various storage chambers. In the simplest case, such a fan can therefore be operated at an irregular or fixed rotational speed.

In particular when a storage chamber is operated cooled, it may be useful to regulate the rotational speed of the fan on the basis of a predetermined temperature difference between the evaporator and the storage chamber, in order thus to adjust the extent of drying of the air in the storage chamber by condensation on the evaporator or the humidity content of the air.

The object is further achieved by a method for operating a refrigeration appliance, as described above, with the steps:

-   -   Enlarging the degree of opening of the second expansion valve         when the temperature in the first storage chamber is above a         target value and/or reducing the degree of opening of the second         expansion valve when the temperature in the first storage         chamber is below a target value.

-   Increasing the rotational speed of the compressor when the     temperature in the second storage chamber is above a target value     and/or reducing the rotational speed when the temperature in the     second storage chamber is below a target value;

-   Opening the first expansion valve when the temperature in the third     storage chamber is above a target value, and/or reducing the degree     of opening of the first expansion valve when the temperature in the     third storage chamber is below a target value,     and by means of a computer program product, which comprises     instructions, which, when executed on a computer, enable this to     operate, as described above, as a control circuit in a refrigeration     appliance or to execute the afore-cited method.

Further features and advantages of the invention result from the description of exemplary embodiments with reference to the appended figures, in which:

FIG. 1 shows a block diagram of an inventive refrigeration appliance; and

FIG. 2 shows a flow chart of an operating method of the refrigeration appliance.

FIG. 1 shows a block diagram of an inventive refrigeration appliance. In a heat-damping housing 1, at least three storage chambers 2, 3, 4 are cut out. Each of these storage chambers 2, 3, 4 is assigned a heat exchanger 5, 6, 7. The assignment can consist for instance in the heat exchanger being embedded in the manner of a cold wall evaporator between an inner container of the storage chamber and a layer of insulation material surrounding the inner container, or in the heat exchanger 5, 6, 7 being assembled in the inner container 8 of the relevant storage chamber 2, 3, 4. In the latter case, a separating wall 9 can be provided in the inner container 8, which separating wall subdivides the volume of the inner container into the storage chambers 2, 3, 4 and a heat exchanger chamber 10 which receives the heat exchangers 5, 6, 7. Irrespective of how the heat exchanger 5, 6, 7 is assigned to the storage chambers 2, 3, 4, a fan 11 can be assigned to each heat exchanger 5, 6, 7 in order to intensify the heat transfer between the storage chambers 2, 3, 4 and their heat exchanger 5, 6, 7. The rotational speed or power of such a fan 11 can be fixedly predetermined or, as explained again more precisely below, can be controlled.

Each storage chamber 2, 3, 4 is equipped with a temperature sensor 12. Measured values of the temperature sensor 12 are detected by a control circuit 13.

A refrigerant circuit comprises, starting from a pressure connection of a compressor 14, in sequence a condenser 15, a pressure line 16, a first expansion valve 17, the heat exchanger 5, a second expansion valve 18, the second heat exchanger 6, the third heat exchanger 7 and a suction line 19, which leads to a suction connection of the compressor 14. The expansion valves 17, 18 are designed in a manner known per se but not described here, in order to maintain a pressure difference, predetermined by a control signal, between the inlet and outlet. The source of the control signals is the control circuit 13. The pressure line 16 and the suction line 19 run on one part of their length in a contrarotating manner in close contact with one another, in order thus to form an internal heat exchanger 22, in which the compressed refrigerant outputs residual heat to the vapor in the suction line 19 shortly before reaching the expansion valve 17.

The pressure difference which can be adjusted on the expansion valve 17 is to a great extent variable. On the one hand, the expansion valve 17 allows a pressure to be adjusted in the heat exchanger 5, which, if at all, only differs minimally from the pressure at the pressure connection of the compressor 14, so that condensation of refrigerant takes place in the heat exchanger 5 and in the condenser 15, and the storage chamber 2 can be operated at a target temperature above the ambient temperature, and refrigerant condensed in the condenser 15 and heat exchanger 5 is supplied to the heat exchangers 6 and 7 by way of the expansion valve 18. An upper limit of the temperature at which the storage chamber 2 can be operated should not amount to below +18° C.

Less high demands are placed on the expansion valve 18: in order to enable operation of the storage chamber 3 as a freezer compartment, even if the storage compartment 2 is operated as a normal refrigerator compartment, a non-negligible drop in pressure on the expansion valve 18 is required. The maximum pressure difference on the expansion valve 18 should be sufficient to also then enable a freezer compartment operation of the storage chamber 3 if essentially the full output pressure of the compressor 14 is present at the input of the expansion valve 18.

There is no appreciable drop in pressure between the heat exchangers 6 and 7. In particular, both heat exchangers 6, 7 and a line connecting them can be manufactured from the same type of pipe with constant cross-sectional dimensions.

Target temperatures for all three storage chambers 2, 3, 4 can be adjusted on a user interface 20 of the control circuit 13. If one of the storage chambers 2, 3, 4 has a fan 11, the possibility can also be provided on the user interface 20 to select an air humidity value for the relevant storage chamber.

FIG. 2 shows a flow chart of an operating method of the control circuit 13. In step S1, the temperatures T2, T3, T4 in the storage chambers 2, 3, 4 are measured with the aid of the sensor 12. In step S2, the target temperature T2 s adjusted for the storage chamber 2 by the user is compared with the ambient temperature T_(env). If the first is lower, i.e. if the storage chamber 2 is cooled, the method moves to step S3.

In step S3, the temperature T2 is compared with the target temperature T2 s. If both values T2, T2 s match within a predetermined tolerance interval, the method moves directly to step S4. If the measured temperature T2 is significantly lower than T2 s, then the control circuit reduces the degree of opening of the expansion valve 18 (S5), in order in this way to increase the pressure or the boiling temperature of the refrigerant in the heat exchanger 5. The reduction in the degree of opening can consist here in increasing the pressure difference to be maintained by the expansion valve 18 between the heat exchangers 5 and 6. Conversely, in step S6, the degree of opening is increased (or the pressure difference is reduced) when the temperature T2 is significantly higher than T2 s.

The extent to which the pressure difference in step S5 or S6 is changed can be a constant or it can take into consideration circumstances such as for instance the sum of the difference between T2 and T2 s or the time taken for the deviation between T2 and T2 s, in order to minimize the time until the match is reestablished between T2 and T2 s or the controller is overshot.

In step S4, the temperature T3 is compared with the target temperature T3 s set by the user for the storage chamber 3. The heat exchanger 6 of the storage compartment 3 always operates as an evaporator; to this end, during operation it is continuously supplied with liquid refrigerant which is either condensed in the condenser 15 and in the heat exchanger 5 is only evaporated to a small extent, or because in the heat exchanger 5 condensation has taken place in addition to that of the condenser. Since the intake pressure of the compressor 14 essentially prevails in the heat exchanger 6 as in heat exchanger 7 and it is well supplied with the liquid refrigerant, the heat exchanger 6 is therefore the coldest of the heat exchangers 5, 6, 7 and T3, T3 s normally lie in a range typical of a freezer compartment which is below −10° C., e.g. approx. −18° C.

If both values T3, T3 s match within a predetermined tolerance interval, the method moves directly to step S7. If the measured temperature T3 is significantly lower than T3 s, then the control circuit 13 reduces the rotational speed of the compressor 14 (S8), in order in this way to increase the pressure or the boiling temperature of the refrigerant in the heat exchanger 6. Conversely, in step S9, the rotational speed is increased when the temperature T3 is significantly higher than T3 s.

The extent to which the rotational speed in step S8 and S9 is changed can be a constant or it can take into consideration circumstances such as for instance the sum of the difference between T3 and T3 s or the time taken for the deviation between T3 and T3 s, in order to minimize the time until the match is reestablished between T3 and T3 s or the controller is overshot.

In step S7, the temperature T4 is compared with the target temperature T4 s adjusted for the storage chamber 4 by the user. If both values T4, T4 s match within a predetermined tolerance interval, the method moves back to step S1 after a predetermined waiting time (S12). If the measured temperature T4 is significantly lower than T4 s, then the control circuit reduces the degree of opening of the expansion valve 17 (S10), in order in this way to reduce the mass flow of the refrigerant and thus to reduce the quantity of liquid refrigerant which reaches the heat exchanger 7. Conversely, in step S11, the degree of opening is increased when the temperature T4 is significantly higher than T4 s so that more liquid refrigerant reaches the heat exchanger 7.

If, by contrast, in step S2, it is determined that heating operation is selected for the storage chamber 2, i.e. when T2 s>T_(env), then T2 is then likewise compared with T2 s (S3′), but when T2 is significantly below T2 s, the expansion valve 17 is opened further (S5′) or when T2 is significantly above T2 s, it is closed again (S6′).

The steps S4, S8, S9 for the temperature regulation in the storage chamber 3 are identical to those described above for the case of cooling operation in the storage chamber 2.

The temperature T4 in the storage chamber 3 is then regulated by way of the expansion valve 18; when it is determined in step S7′ that this is lower than the target temperature T4 s, then the degree of opening of the expansion valve 18 is reduced, in order to reduce the availability of liquid refrigerant in the heat exchanger 7 (S10′); in the opposite case (S11′), the degree of opening is enlarged.

If desired, a fan 21 can be arranged on the condenser 15 in order to blow ambient air via the condenser 15 and thus to accelerate the heat dissipation via the condenser 15. The fan 21 can run at a fixed rotational speed. It is also conceivable for the control circuit 13 to vary its rotational speed in the same direction as that of the compressor 14 or with the ambient temperature, in order to take into account the drop in pressure at the condenser 15 which has increased with an increased compressor power.

The rotational speeds of the fan 11 are independent of the temperatures in the storage chambers 2, 3, 4 and the ambient temperature. They can be fixedly predetermined; particularly in the case of the storage chamber 4 which can be used as a normal refrigeration compartment, it may be expedient to provide the selection between various power stages or rotational speeds of the fan 11 there to the user at the interface 20. The higher the power of the fan 11, the lower therefore the temperature difference between the storage chamber 4 and the evaporator 7, which is sufficient to maintain the target temperature T4 s of the storage chamber 4. And the higher the temperature of the heat exchanger 7, the smaller therefore the portion of air humidity from the storage chamber 4, which condenses on the heat exchanger 7 and has to be sent into the atmosphere. A high fan power is therefore suited to the storage of refrigerated goods which are sensitive to drying. For refrigerated goods which tend to form mold or suchlike with high humidity, a lower fan power can be adjusted.

The same considerations apply to the control of the fan 11 in the storage chamber 2, when this is used as a normal refrigerator compartment or in a temperature range adjacent thereto, for instance as a fresh refrigerator compartment.

In order to be able to create ideal storage conditions both for refrigerated goods which are sensitive to drying and also to wet, it may be desirable to have more than the three storage compartments shown in FIG. 1 available in a refrigeration appliance. In order to cool or heat such a further storage chamber, the refrigerant circuit can have a plurality of line sections, each of which extends between connecting points 23 of the pressure line 16 and 24 of a line connecting the expansion valve 18 with the heat exchanger 6, of which each, similarly to the components 17, 5, 18, sequentially have an upstream expansion valve, a heat exchanger for the further storage chamber and a downstream expansion valve.

REFERENCE CHARACTERS

-   1 Housing -   2 Storage chamber -   3 Storage chamber -   4 Storage chamber -   5 Heat exchanger -   6 Heat exchanger -   7 Heat exchanger -   8 Inner container -   9 Separating wall -   10 Heat exchanger chamber -   11 Fan -   12 Temperature sensor -   13 Control circuit -   14 Compressor -   15 Condenser -   16 Pressure line -   17 Expansion valve -   18 Expansion valve -   19 Suction line -   19 User interface -   21 Fan -   22 Internal heat exchanger -   23 Connection point -   24 Connection point 

1-13. (canceled)
 14. A refrigeration appliance or household refrigeration appliance, comprising: at least first, second and third storage chambers; a compressor having a pressure connection and a suction connection; a refrigerant circuit; connected to said refrigerant circuit in series one behind another between said pressure connection and said suction connection of said compressor: a condenser, a first expansion valve, a first heat exchanger of said first storage chamber, a second expansion valve, a second heat exchanger of said second storage chamber, and a third heat exchanger of said third storage chamber, said third heat exchanger connected in series downstream of said second heat exchanger; and a control circuit for controlling operation of said compressor and said expansion valves, said control circuit configured to maintain a higher storage temperature in said third storage chamber than in said second storage chamber.
 15. The refrigeration appliance according to claim 14, wherein said second and said third heat exchangers are connected to one another without an intermediate restriction.
 16. The refrigeration appliance according to claim 14, wherein said compressor has a rotational speed being adjustable to a plurality of values or being continuously adjustable, and said control circuit is configured to at least one of increase the rotational speed when a temperature of said second storage chamber is above a target value or reduce the rotational speed when the temperature of said second storage chamber is below a target value.
 17. The refrigeration appliance according to claim 14, wherein said control circuit is configured to at least one of enlarge a degree of opening of said first expansion valve when a temperature in said third storage chamber is above a target value or reduce the degree of opening of said first expansion valve when the temperature in said third storage chamber is below a target value.
 18. The refrigeration appliance according to claim 14, wherein said control circuit is configured to at least one of enlarge a degree of opening of said second expansion valve when a temperature of said third storage chamber is above a target value or reduce the degree of opening of said second expansion valve when the temperature of said third storage chamber is below a target value.
 19. The refrigeration appliance according to claim 14, wherein said control circuit is configured to at least one of enlarge a degree of opening of said second expansion valve when a temperature in said first storage chamber is above a target value or reduce the degree of opening of said second expansion valve when the temperature in said first storage chamber is below a target value.
 20. The refrigeration appliance according to claim 14, wherein said control circuit is configured to at least one of enlarge a degree of opening of said first expansion valve when a temperature in said first storage chamber is below a target value or reduce the degree of opening of said first expansion valve when the temperature in said first storage chamber is above a target value.
 21. The refrigeration appliance according to claim 14, wherein said control circuit is configured, upon a deviation of a temperature of said third storage chamber from a target value, to select an expansion valve to be adjusted as a function of whether a target temperature of said first storage chamber is above or below an ambient temperature.
 22. The refrigeration appliance according to claim 14, which further comprises a third expansion valve, a fourth storage chamber, a fourth heat exchanger of said fourth storage chamber and a fourth expansion valve being connected in series with one another and in parallel with said first expansion valve, said first heat exchanger and said second expansion valve.
 23. The refrigeration appliance according to claim 14, which further comprises at least one fan associated with at least one of said heat exchangers for driving an air exchange between said at least one heat exchanger and at least one of said storage chambers.
 24. The refrigeration appliance according to claim 23, wherein said control circuit is configured to regulate a rotational speed of said at least one fan based on a predetermined temperature difference between one of said heat exchangers and one of said storage chambers associated with said one of said storage chambers.
 25. A method for operating a refrigeration appliance or household refrigeration appliance, the method comprising: providing a refrigeration appliance or household refrigeration appliance according to claim 14; at least one of enlarging a degree of opening of said second expansion valve when a temperature of said first storage chamber is above a target value or reducing the degree of opening of said second expansion valve when the temperature in the first storage chamber is below a target value; at least one of increasing a rotational speed of said compressor when a temperature in said second storage chamber is above a target value or reducing the rotational speed of said compressor when the temperature in said second storage chamber is below a target value; and at least one of enlarging the degree of opening of said first expansion valve when a temperature in said third storage chamber is above a target value or reducing the degree of opening of said first expansion valve when the temperature in said third storage chamber is below a target value.
 26. A non-transitory computer program product with instructions stored thereon, that when executed by a computer, operates as said control circuit in the refrigeration appliance or household refrigeration appliance according to claim
 14. 27. A non-transitory computer program product with instructions stored thereon, that when executed by a computer, performs the method according to claim
 25. 